- 1Leeds University, Earth and Environment, Leeds, United Kingdom of Great Britain – England, Scotland, Wales (a.m.mccaig@leeds.ac.uk)
- 2School of Earth and Environmental Sciences, Cardiff University; Cardiff, United Kingdom.
- 3Department of Geology and Geophysics, Woods Hole Oceanographic Institution; Woods Hole MA USA.
- 4International Ocean Discovery Program, Texas A&M University; College Station TX, USA.
- *A full list of authors appears at the end of the abstract
IODP Expedition 399 drilled a record 1268m hole (U1601C) in the Atlantis Massif oceanic core complex, sampling serpentinised harzburgites and dunites, cut by a gabbro net-vein complex (Lissenberg et al., 2024). The near ridge environment of the Atlantis Massif, and the well constrained exhumation of the section by detachment faulting (Escartin et al., 2022), allows us to constrain the recent (~6 million year) history of this important section of abyssal peridotites exceptionally well. In addition, Site U1601 is located only 800 m from the Lost City hydrothermal field (LCHF), which vents warm (40-115 °C) alkaline fluids rich in H2 and CH4. The section allows direct comparison with the LCHF substrate and reactions occurring deep in the massif, together with extremophile microbiology and abiotic organic synthesis.
Here we focus on the history of the section, beginning with partial melting in the upwelling asthenosphere beneath the mid-Atlantic ridge, inferred to have begun at ~ 60km depth (Olive, 2023) and ~ 6 m.y. ago based on a half-spreading rate of 11.8 mm/yr. It is important to recognise that detachment faulting involves rotation of the fault and footwall. The detachment fault captures part of the mid-ocean ridge corner flow translating vertical upwelling into horizontal plate motion. The current near-vertical section collected by drilling was therefore plunging at a low angle until incorporated into the lithosphere and rotated by faulting. The section contains numerous dunitic veins inferred to be melt pathways forming in the upwelling asthenosphere. Dips of these veins peak at ~45° in the core reference frame, suggesting they were neither vertical nor horizontal in the rotated section. Further upwelling led to incorporation of the section into the lithosphere in the footwall of the nascent detachment fault, at a depth of 7-10 kmbsf. The next event was intrusion of a net vein complex of gabbros, with 265 logged units, mostly < 1 m in thickness. Significant mylonitic deformation is seen along the margins of many of these gabbros. During further uplift towards the seafloor, intense hydrothemal alteration of the gabbros and serpentinisation of the harzburgites and dunites occurred at temperatures < 400 °C, and the section was first exposed on the seafloor at ~ 600 kyr (Escartin et al., 2022), with the detachment fault rotating to a subhorizontal dip. Following this, a local low temperature overprint leading to oxidation of magnetite and locally high uranium contents is observed in the upper 200m of the core.
The history outlined above offers a framework for understanding the full range of magmatic, deformation, alteration and microbiological processes in the upwelling mantle at a slow spreading ridge, including new constraints on processes in the substrate of the LCHF.
Escartin et al., (2022). Tectonic termination of oceanic detachment faults, with constraints on tectonic uplift and mass wasting related erosion rates.Earth and Planetary Science Letters 584, 117449
Lissenberg et al., (2024). A long section of serpentinized depleted mantle peridotite. Science. 623-629 385.6709
Olive (2023) Mid-Ocean Ridges: Geodynamics Written in the Seafloor DOI 10.1016/B978-0-323-85733-8.00018-4
Andrew McCaig(1). Susan Q. Lang; Department of Geology and Geophysics, Woods Hole Oceanographic Institution, USA. Peter Blum; International Ocean Discovery Program, Texas A&M University, USA. Natsue Abe; Agency for Marine-Earth Science and Technology, Japan. William Brazelton; School of Biological Sciences, University of Utah, USA. Rémi Coltat; Geosciences Department, Ecole Normale Supérieure, Paris, France and Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Spain. Jeremy R. Deans; School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, USA. Kristin L. Dickerson; Department of Earth and Planetary Sciences, University of California, Santa Cruz, USA. Marguerite Godard; Department of Geosciences, University of Montpellier, France. Barbara E. John; Department of Geology and Geophysics, University of Wyoming, USA. Frieder Klein; Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, USA. Rebecca Kuehn; Institute of Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Germany. Kuan-Yu Lin; Department of Earth Sciences, University of Delaware, USA. C. Johan Lissenberg; School of Earth and Environmental Sciences, Cardiff University, United Kingdom. Haiyang Liu; Institute of Oceanology, Chinese Academy of Sciences, China. Ethan L. Lopes; Department of Geophysics, Stanford University, USA. Toshio Nozaka; Department of Earth Sciences, Okayama University, Japan. Andrew J. Parsons; School of Geography, Earth, and Environmental Sciences, University of Plymouth, United Kingdom. Vamdev Pathak; Department of Geology, Central University of Punjab, India. Mark K. Reagan; Department of Earth and Environmental Sciences, University of Iowa, USA. Jordyn A. Robare; School of Molecular Sciences, Arizona State University, USA. Ivan Savov(1). Esther Schwarzenbach; University of Fribourg, Switzerland. Olivier J. Sissmann; 1 et 4 avenue de Bois-Preau 75005 Paris, France. Gordon Southam; Earth and Environmental Sciences, The University of Queensland, Australia. Fengping Wang; International Center for Deep Life Investigation (IC-DLI), Shanghai, Jiao Tong University, China. C. Geoffrey Wheat; College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, USA. Lesley Anderson; United States Antarctic Program, USA. Sarah N.R. Treadwell; Department of Communication, University of North Dakota and Blue Marble Space Institute, USA.
How to cite: McCaig, A., Lissenberg, J., Lang, S., and Peter, B. and the International Ocean Discovery Program Expedition 399 Science Party: IODP Expedition 399: the six million year uplift history of a record-breaking section of depleted mantle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18332, https://doi.org/10.5194/egusphere-egu25-18332, 2025.
